Various blood processing systems now make it possible to collect particular blood constituents, rather than whole blood, from a blood source. Typically, in such systems, whole blood is drawn from a blood source, the particular blood component or constituent is separated, removed, and collected, and the remaining blood constituents are returned to the blood source. Removing only particular constituents is advantageous when the blood source is a human donor or patient, because potentially less time is needed for the donor's body to return to pre-donation levels, and donations can be made at more frequent intervals than when whole blood is collected. This increases the overall supply of blood constituents, such as plasma and platelets, made available for transfer and/or therapeutic treatment.
Whole blood is typically separated into its constituents through centrifugation. This requires that the whole blood be passed through a centrifuge after it is withdrawn from, and before it is returned to, the blood source. To avoid contamination and possible infection (if the blood source is a human donor or patient), the blood is preferably contained within a sealed, sterile fluid flow system during the entire centrifugation process. Typical blood processing systems thus include a permanent, reusable assembly containing the hardware (centrifuge, drive system, pumps, valve actuators, programmable controller, and the like) that spins and pumps the blood, and a disposable, sealed, and sterile flow circuit that is mounted in cooperation on the hardware.
The centrifuge engages and spins the disposable flow circuit during a blood separation step. As the flow circuit is spun by the centrifuge, the heavier (greater specific gravity) components of the whole blood in the flow circuit, such as red blood cells, move radially outwardly away from the center of rotation toward the outer or “high-G” wall of the centrifuge. The lighter (lower specific gravity) components, such as plasma, migrate toward the inner or “low-G” wall of the centrifuge. Various ones of these components can be selectively removed from the whole blood by providing appropriately located channeling seals and outlet ports in the flow circuit. For example, in one blood separation procedure, plasma is separated from cellular blood components and collected, with the cellular blood components and a replacement fluid being returned to the blood source.
One disadvantage of known systems is that they may not include adequate safeguards to ensure that the proper disposable flow circuit is used and that the disposable flow circuit is properly aligned within the centrifuge. If an inappropriate flow circuit is used with the centrifuge (or if the flow circuit is improperly installed), damage can be done to the flow circuit and/or the centrifuge. Even if the flow circuit and centrifuge are not damaged, the blood may be improperly fractionated and processed, which reduces the effectiveness of the system and can even be harmful to a human connected to the system.
It is known to employ an optical sensor system to monitor the flow of blood and/or blood components through the flow circuit in the centrifuge and determine various characteristics of the flow. These optical sensor systems can be characterized as either one- or two-dimensional types. In comparison to known systems, it may be advantageous to provide an optical monitoring system with improved flow control functionality, additional functionality (beyond flow control), and/or alternative placement within a blood separation device.